Tides from Moon–Sun position, and sea waves
GeographyWater & OceansAges 15–16
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Water & Oceans
Viewed from above the North Pole: the pull of the Moon and Sun heaps ocean water into two tidal bulges; as Earth spins, a coastal point (red dot) meets high water and low water about twice a day (period 12 h 25 min). Drag the Moon around its orbit: when Moon, Sun and Earth line up (new moon, full moon) it is spring tide, when they are at right angles (half moon) it is neap tide; a 3-day water-level graph updates continuously. The panel below models wind-driven sea waves — change wind speed and depth to see how height, wavelength, period and breaking waves near shore change.
Lesson: Ocean and sea water: sea waves, tides
What it shows
Tides are the regular rise and fall of sea level caused mainly by the Moon's gravity, with a smaller effect from the Sun. Ocean water piles up in two bulges, one facing the Moon and one on the far side, so a coastal point passes through two high tides and two low tides roughly every 24 h 50 min. When Sun, Earth and Moon line up at new and full moon, the pulls add to give spring tides; at first and last quarter they partly cancel, giving neap tides.
How to use
Drag the Moon around its orbit to a new moon, first quarter or full moon position and watch the red coastal dot and the 3-day water-level graph. Use Speed to run several days quickly and compare the tidal range at spring and neap tide. With Show sea wave model on, change Wind and Depth of offshore waters to see wave height, period and wavelength change and where waves break near the shore.
Parameters you can change
- Moon position at start (0 = new moon, 90 = first quarter, 180 = full moon) 0–359 °
- Simulation speed 0.5–24 hours/second
- Wind speed over the sea 2–25 m/s
- Depth of offshore waters 2–60 m
- Show sea wave model
Questions to explore
- At which Moon phases is the tidal range largest, and why?
- Why do neap tides happen when the Moon is at first or last quarter?
- When the wind speed doubles, how do the wave height and wave period change?
